CA1083344A - Procedure for drying an organic, most appropriately a xylogenic material, such as veneers for instance - Google Patents
Procedure for drying an organic, most appropriately a xylogenic material, such as veneers for instanceInfo
- Publication number
- CA1083344A CA1083344A CA297,546A CA297546A CA1083344A CA 1083344 A CA1083344 A CA 1083344A CA 297546 A CA297546 A CA 297546A CA 1083344 A CA1083344 A CA 1083344A
- Authority
- CA
- Canada
- Prior art keywords
- air
- drying
- damper
- drying chamber
- procedure
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Drying Of Solid Materials (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A procedure for drying organic materials, including xylogenic materials originating from wood, such as veneers, by means of hot circulating air which circulates in a drying chamber from a blower to a heat exchanger, passing by the organic material, collecting the water vapour released there-from, and continuing to the blower, whereafter part of the air/water vapour mixture is conducted through a vent, throttled by means of a damper, into the free atmosphere. In the drying chamber the temperature and pressure are monitored and the damper is used to control the quantity of the vented air so that there is a continuous predetermined vacuum in the drying chamber.
A procedure for drying organic materials, including xylogenic materials originating from wood, such as veneers, by means of hot circulating air which circulates in a drying chamber from a blower to a heat exchanger, passing by the organic material, collecting the water vapour released there-from, and continuing to the blower, whereafter part of the air/water vapour mixture is conducted through a vent, throttled by means of a damper, into the free atmosphere. In the drying chamber the temperature and pressure are monitored and the damper is used to control the quantity of the vented air so that there is a continuous predetermined vacuum in the drying chamber.
Description
~0833~4 This invention relates to a procedure for drying materials containing water and more particularly to an improved procedure in which reduced hea-t energy is used.
At present, heat energy is unnecessarily wastedin veneer drying, due to the fact that the conditions of the drying process vary considerably. Influencing factors are veneer quality, the degree to which drying apparatus is filled, and the like. Notwithstanding such variations, an adjustable circulating air vent damper in known drying apparatus is kept in a position such that the apparatus intermittently releases to the atmosphere the gases and water vapour produced in the drying process. The result hereof is a situation wherein the vent damper is in a theoretical optimum position during short intervals only as regards heat economy, while being opened unnecessarily wide the greater part of the time, thus letting thermal energy escape from the drying process.
As a result of the foregoing, the water content of the circulating air is commonly in a range of from 80 to 110 kg H2O per kg of dry air. In such case between 30 and 40% of the total heat energy consumed is used to heat replacement air.
If the vent damper is controlled so that it is constantly in its optimum position whereby the requirement for replacement air is minimized, it is possible to reduce the amount of heat energy that has to be consumed to heat the replacement air. Theoretically, the heat energy reduction is nearly all of the above-men-tioned 30 tO 40%. Since the thermal energy consumption of the drying apparatus is, depending on its capacity, 15 to 28 x 103 Gcal per year, a conserva-tive calculation shows that the annual savinys can be 15%, or -- 1 -- , . ~
~083344 between 2250 and 4200 Gcal per year; (6000 hrs x 2.5 m /hr to 6000 hrs x 5 m3/hr) x 0.95 Gcal per m3 of dry veneer.
The disadvantages of the prior art may be sub-stantially overcome and the foregoing advantages achieved by recourse to the invention which relates to an improvement in a procedure for drying an organic xylogenic material, including veneers, with hot circulating air that circulates from a blower to a heat exchanger in a drying chamber, passing by the organic material, collecting the water vapour released there-from, and continuing back to the blower, wherea~ter part ofthe mixture of air and water vapour is conducted through a venting aperture throttled by means of a damper and into the free atmosphere. The improvement comprises the steps of, monitoring the temperature and pressure of the drying chamber, and operating the damper to control the quantity of vented air so that there is a continuous pre~e-ter~ined vacuum in the chamber.
When the water content of the circulating air is high, thermal energy is transferred from the circulating air to the veneer with considerably greater efficiency than from dry circulating air. The veneer that is being dried will then heat up rapidly, and the evaporation of the water present in the veneer starts quite clearly sooner than in a dry atmosphere.
In this way drying of the veneer is speeded up.
An advantageous embodiment of the invention utilizes the pressure in a drying chamber to predetermine the humidity of the circulating air, a vent damper being controlled so as to maintain the humidity of the circulating air within 250 -to 400 g H2O per kg of dry air. Keeping the humidi-ty of the circulating air within these limits, the best results in veneer drying are obtained.
The invention will now be more particularly de-scrihed with reference to an embodiment thereof shown, by way of example, in the accompanying drawing which is a diagrammatic representation of drying apparatus that is particularly adapted to function according to -the procedure of the in-; vention.
The drying apparatus 1 comprises a circulating airblower 3, a heating element 4, nozzle boxes 5, and a vacuum chamber 9, wherein the circulating air circulates. The apparatus also comprises a ventpipe 6 for removing water vapour and other gases resulting from the drying process. It will be noted that the pipe 6 contains a gas venting regulating ~;
damper 7. The position of the damper 7 is controlled by means of an action means 8, which receives an actuating signal from a control unit 11 that is connected to a sensor 10 in the chamber 9. The material to be dried, veneer sheets in the embodiment illustrated, is disposed between the nozzle boxes 5.
During operation of the apparatus 1, the blower 3 draws circulating air from the chamber 9 and feeds it through the heater 4 into the nozzle boxes 5. At the same time, part of the circulating air is vented through the vent pipe 6. The ~uantity of air thus removed may be controlled by means of the damper 7. Adjustment of this damper has a direct effect on the vacuum prevailing in the chamber 9.
The vacuum in the chamber 9 is monitored by means of the sensor 10, and the pressure reading obtained is used to control the position of the yas ven-ting damper 7. The vacuum in the chamber 9 is maintained at a predetermined magnitude which just prevents the gases en-trained ln the circula~ing air from escaping to the free atmosphere. .
In the apparatus 1 the sensor 10 monitors the pressure (the vacuum within the machine) at a point where replacement air flows in from the atmosphere. It will be understood that this point lies in the immediate vicinity of air inlet apertures 2 via which material to be dried enters the chamber 9. When the said pressure is measured and is compared with the atmospheric pressure at an equivalent point outside the apparatus 1, the differential pressure between the exterior and interior of the apparatus is found, which cor-relates directly with the replacement air rate. When this differential pressure is regulated, by throttling the air vent passage 6, to be such that the replacement air flow rate is at a level at which the replacement air effects only partial dilution of the circulating air, the humidity of the circu-lating air can be accurately controlled.
Following the procedure of the invention the replacement air quantity is minimized by keeping the venting damper in that particular position which results in a low differential pressure between the outside and inside of the apertures 2. The quantity of the replacement air flowing into the apparatus correlates directly with the said differential pressure. As water evaporates in the drying space, the partial pressure of water vapour and the gas pressure both increase.
The sensor 10 detects the rise of pressure and generates -the signal that operates the controller 11, which opens or closes the vent damper 7 so that the differential pressure at the apertures 2 remains constant and the quantity of lnflowing replacement air is maintained at a low level as required.
Having regard to -the description and illustrated 1~8334~
embodiment of the present invention, it will be apparent to those skilled in the art that variations thereof within the scope of the invention are readily feasible. Accordingly, the disclosed and illustrated embodiment herein should be considered as exemplary rather than restrictive of the invention which is' defined in the accompanying claims.
At present, heat energy is unnecessarily wastedin veneer drying, due to the fact that the conditions of the drying process vary considerably. Influencing factors are veneer quality, the degree to which drying apparatus is filled, and the like. Notwithstanding such variations, an adjustable circulating air vent damper in known drying apparatus is kept in a position such that the apparatus intermittently releases to the atmosphere the gases and water vapour produced in the drying process. The result hereof is a situation wherein the vent damper is in a theoretical optimum position during short intervals only as regards heat economy, while being opened unnecessarily wide the greater part of the time, thus letting thermal energy escape from the drying process.
As a result of the foregoing, the water content of the circulating air is commonly in a range of from 80 to 110 kg H2O per kg of dry air. In such case between 30 and 40% of the total heat energy consumed is used to heat replacement air.
If the vent damper is controlled so that it is constantly in its optimum position whereby the requirement for replacement air is minimized, it is possible to reduce the amount of heat energy that has to be consumed to heat the replacement air. Theoretically, the heat energy reduction is nearly all of the above-men-tioned 30 tO 40%. Since the thermal energy consumption of the drying apparatus is, depending on its capacity, 15 to 28 x 103 Gcal per year, a conserva-tive calculation shows that the annual savinys can be 15%, or -- 1 -- , . ~
~083344 between 2250 and 4200 Gcal per year; (6000 hrs x 2.5 m /hr to 6000 hrs x 5 m3/hr) x 0.95 Gcal per m3 of dry veneer.
The disadvantages of the prior art may be sub-stantially overcome and the foregoing advantages achieved by recourse to the invention which relates to an improvement in a procedure for drying an organic xylogenic material, including veneers, with hot circulating air that circulates from a blower to a heat exchanger in a drying chamber, passing by the organic material, collecting the water vapour released there-from, and continuing back to the blower, wherea~ter part ofthe mixture of air and water vapour is conducted through a venting aperture throttled by means of a damper and into the free atmosphere. The improvement comprises the steps of, monitoring the temperature and pressure of the drying chamber, and operating the damper to control the quantity of vented air so that there is a continuous pre~e-ter~ined vacuum in the chamber.
When the water content of the circulating air is high, thermal energy is transferred from the circulating air to the veneer with considerably greater efficiency than from dry circulating air. The veneer that is being dried will then heat up rapidly, and the evaporation of the water present in the veneer starts quite clearly sooner than in a dry atmosphere.
In this way drying of the veneer is speeded up.
An advantageous embodiment of the invention utilizes the pressure in a drying chamber to predetermine the humidity of the circulating air, a vent damper being controlled so as to maintain the humidity of the circulating air within 250 -to 400 g H2O per kg of dry air. Keeping the humidi-ty of the circulating air within these limits, the best results in veneer drying are obtained.
The invention will now be more particularly de-scrihed with reference to an embodiment thereof shown, by way of example, in the accompanying drawing which is a diagrammatic representation of drying apparatus that is particularly adapted to function according to -the procedure of the in-; vention.
The drying apparatus 1 comprises a circulating airblower 3, a heating element 4, nozzle boxes 5, and a vacuum chamber 9, wherein the circulating air circulates. The apparatus also comprises a ventpipe 6 for removing water vapour and other gases resulting from the drying process. It will be noted that the pipe 6 contains a gas venting regulating ~;
damper 7. The position of the damper 7 is controlled by means of an action means 8, which receives an actuating signal from a control unit 11 that is connected to a sensor 10 in the chamber 9. The material to be dried, veneer sheets in the embodiment illustrated, is disposed between the nozzle boxes 5.
During operation of the apparatus 1, the blower 3 draws circulating air from the chamber 9 and feeds it through the heater 4 into the nozzle boxes 5. At the same time, part of the circulating air is vented through the vent pipe 6. The ~uantity of air thus removed may be controlled by means of the damper 7. Adjustment of this damper has a direct effect on the vacuum prevailing in the chamber 9.
The vacuum in the chamber 9 is monitored by means of the sensor 10, and the pressure reading obtained is used to control the position of the yas ven-ting damper 7. The vacuum in the chamber 9 is maintained at a predetermined magnitude which just prevents the gases en-trained ln the circula~ing air from escaping to the free atmosphere. .
In the apparatus 1 the sensor 10 monitors the pressure (the vacuum within the machine) at a point where replacement air flows in from the atmosphere. It will be understood that this point lies in the immediate vicinity of air inlet apertures 2 via which material to be dried enters the chamber 9. When the said pressure is measured and is compared with the atmospheric pressure at an equivalent point outside the apparatus 1, the differential pressure between the exterior and interior of the apparatus is found, which cor-relates directly with the replacement air rate. When this differential pressure is regulated, by throttling the air vent passage 6, to be such that the replacement air flow rate is at a level at which the replacement air effects only partial dilution of the circulating air, the humidity of the circu-lating air can be accurately controlled.
Following the procedure of the invention the replacement air quantity is minimized by keeping the venting damper in that particular position which results in a low differential pressure between the outside and inside of the apertures 2. The quantity of the replacement air flowing into the apparatus correlates directly with the said differential pressure. As water evaporates in the drying space, the partial pressure of water vapour and the gas pressure both increase.
The sensor 10 detects the rise of pressure and generates -the signal that operates the controller 11, which opens or closes the vent damper 7 so that the differential pressure at the apertures 2 remains constant and the quantity of lnflowing replacement air is maintained at a low level as required.
Having regard to -the description and illustrated 1~8334~
embodiment of the present invention, it will be apparent to those skilled in the art that variations thereof within the scope of the invention are readily feasible. Accordingly, the disclosed and illustrated embodiment herein should be considered as exemplary rather than restrictive of the invention which is' defined in the accompanying claims.
Claims (2)
EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS
FOLLOWS:
1. An improvement in a procedure for drying an organic xylogenic material, including veneers, with hot circu-lating air that circulates from a blower to a heat exchanger a drying chamber, passing by the organic material, collecting water vapour released therefrom, and continuing back to the blower, whereafter part of the mixture of air and water vapour is conducted through a venting aperture throttled by means of a damper and into the free atmosphere, the improvement comprising the steps of, monitoring the temperature and pressure of the drying chamber, and operating the damper to control the quantity of vented air so that there is a continuous pre-determined vacuum in said chamber.
2. An improved procedure as claimed in Claim 1, wherein the humidity of the circulating air is determined by the pressure in the drying chamber and by controlling the damper, the humidity of the circulating air being kept within a range of from 250 to 400 g H2O per kg of dry air.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA297,546A CA1083344A (en) | 1978-02-23 | 1978-02-23 | Procedure for drying an organic, most appropriately a xylogenic material, such as veneers for instance |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA297,546A CA1083344A (en) | 1978-02-23 | 1978-02-23 | Procedure for drying an organic, most appropriately a xylogenic material, such as veneers for instance |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1083344A true CA1083344A (en) | 1980-08-12 |
Family
ID=4110845
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA297,546A Expired CA1083344A (en) | 1978-02-23 | 1978-02-23 | Procedure for drying an organic, most appropriately a xylogenic material, such as veneers for instance |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1083344A (en) |
-
1978
- 1978-02-23 CA CA297,546A patent/CA1083344A/en not_active Expired
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| Date | Code | Title | Description |
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| MKEX | Expiry |